Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Common raven physiology wikipedia , lookup
Cardiac output wikipedia , lookup
Resting potential wikipedia , lookup
Homeostasis wikipedia , lookup
Stimulus (physiology) wikipedia , lookup
Haemodynamic response wikipedia , lookup
Countercurrent exchange wikipedia , lookup
Electrophysiology wikipedia , lookup
Transvascular and interstitial transport Tissue Engineering & Drug Delivery BBI 4203 LECTURE #12 Vascular permeability • Capacity of a blood vessel wall to allow for the flow of small molecules (ions, water, nutrients) or even whole cells (lymphocytes on their way to the site of inflammation) in and out of the vessel. • Flux across membrane J=P*S*∆C – J= rate of mass flow kg/s (not kg/m2*s) – S= vessel wall surface area in m2 – ∆C= pressure difference across vessel wall in kg m-3 • Permeability coefficient P=J/(S*∆C) (m s-1) – units of distance per unit time Vascular permeability varies • Blood vessel walls are lined by a single layer of endothelial cells. • The gaps between endothelial cells (cell junctions) are strictly regulated depending on the type and physiological state of the tissue. • Blood-brain barrier has tight endothelial cell junctions • Arteries and veins are intended for blood transport, have thicker walls, and are less permeable • Capillaries or microvessels are the most permeable Microvessels is a tube comprised of 1-3 endothelial cells and basement membrane Cross-section of microvessel I. Structure of the microvessel wall: * Glycocalyx: fibrous chains of the membrane glycoproteins with negative charge. Thickness is 100 ~ 400 nm. * Basement membrane: An electrodense fiber matrix layer, containing type IV collagen, proteoglycan (e.g., perlecan), laminin, fibronectin, and glycoproteins. BM Extravasation of D20 in the rabbit granulation tissue Extravasation of D20 in the rabbit granulation tissue 1 min 5 min 20 min 10 min 40 min • What are the major barriers for transvascular transport? • Endothelial layer • Glycocalyx • What are paths available for transport across the microvessel wall? • What are cutoff sizes of pores for drug and gene delivery across microvessel wall? Endothelial cell junctions: • tight junction: - claudins, occludin, - junctional adhesion molecule (JAM) family, - nectin, - endothelial cell selective adhesion molecule (ESAM). Dejana, J., NATURE REV | MOL CELL BIOL, 5: 263, 2004. • adhesion junctions: - vascular endothelial cadherin (VE-cadherin) - vascular endothelial protein tyrosine phosphatase (VEPTP) modulates cadherin phosphorylation - Adhesion junction is enhanced by platelet endothelial cell adhesion molecule (PE-CAM). - Adhesion to pericytes and smooth muscle cells is mediated by neuronal cadherin (Ncadherin) 1. Pathways for transendothelial transport (i) Continuous capillary (i) Direct diffusion through cells https://www.stu.qmul.ac.uk/SMD/ kb/microanatomy/cardiovascular/ index.htm Molecule EC Cellular Junction EC (ii) Vesicular pathways (a) Transendothelial vesicles (shuttles) (b) Fusion-fission of vesicles (c) Transendothelial vesicular channels (iii) Diffusion along the cell membrane 2. Fenestrated capillary (e.g., in the kidney, pancreas, adrenal cortex, and choroid in the eye) In addition to the pathways in continuous capillaries, molecules can cross endothelial cells through diaphragmed or open fenestrae (~100 nm) within the EC. Diaphragmed fenestrae EC Open fenestrae Basement membrane Peritubular capillary in renal tube A Thin sections of the peritubular capillary shows single and double diaphragms bridging the fenestral pores. Fenestral diaphragms on the luminal surface of peritubular capillary in the rat kidney cortex B BEARER, E.L. AND ORCI, L., J CELL BIOL 100:418-428, 1985. 3. Discontinuous capillary (e.g., in the liver, spleen, bone marrow, and solid tumors) In addition to the pathways in continuous capillaries, molecules can cross endothelial cells through open gaps. Liver https://www.stu.qmul.ac.uk/SMD/kb/microanato my/cardiovascular/index.htm Open intercellular gaps Basement membrane (partial or total absence) II. Quantitative analysis of transvascular transport (1) Phenomenological approach (a) Flux of fluid JV LP S (p s ) Starling's law of filtration spaces) where: Jv - rate of fluid flow, LP - hydraulic conductivity (ease with which fluid flows thru interstitial S - surface area of the endothelium p - hydrostatic pressure difference π - osmotic pressure difference s - osmotic reflection coefficient (A) Starling's law presented in physiology textbooks JV LP S (p s ) In the arterial end pv = 35 mmHg, pi = - 2 mmHg; v = 28 mmHg, i = 0.1 mmHg Assume LpS same for both arterial and venous sides and that s = 1.0 pnet = (pv - pi) - s(v - i) = 9.1 mmHg => Filtration In the venous end pv = 15 mmHg, pi = - 2 mmHg; v = 28 mmHg, i = 3 mmHg pnet = (pv - pi) - s(v - i) = -8.0 mmHg => Reabsorption Microvessel filtration and resorption Arterial side Net fluid outflow Hydrostatic pressure dominates Venous side Net fluid inflow Osmotic pressure dominates (b) Flux of solute Factors that affect solute motion in addition to fluid flux _ J S JV (1 f ) CS PSC (Kedem and Katchalsky equation 1958) where: JS - rate of solute transport, f - filtration reflection coefficient (Note: in general f s) _ C S - average molar concentration within the membrane P - microvascular permeability coefficient S – surface area C - concentration difference (c) Phenomenological constants in transvascular transport Hydraulic permeability J /S fluid flux LP V p CS 0 hydrostati c pressure difference CS 0 Permeability coefficient solute flux J /S P S C JV 0 concentrat ion difference JV 0 Osmotic reflection coefficient S Filtration reflection coefficient hydrostati c pressure difference p JV 0 osmotic pressure difference JV 0 JS / S solute flux across vessel wall 1 ( J C ) / S solute flux in the solution C 0 V 0 C 0 f 1 (IV) Measurement of microvascular permeability inject fluorescent dye into vessel and then flush it out Fluorescent intensity in tissue Saline Fluorescence dye Measure time it takes for maximum fluorescence to be reached. Shorter time means more permeable Vessel permeability v a c LS174T tumor tissue Normal mouse s.c. tissue Microvascular Permeability -8 10 cm/sec 1000 Normal Tissue Tumor Tissue 100 10 1 0.1 Dextran 150 ~ 10 nm BSA ~ 7 nm Liposome ~ 90 nm Molecular size cutoff of pores in different tumor vessels (sieving effect) 2000 1500 1000 MCa IV ST- 12 LS174T HCa I 0 ST-8 500 Shionogi Liposome Size (nm) 2500 Hobbs, et al, PNAS, 1998 Factors that affect the transvascular transport Size, charge, configuration (shape), polarity of molecules Size and density of pores in the vascular endothelium Density of the extracellular matrix (e.g., glycocalyx, BM) Concentration and pressure differences across the vessel wall Concentration of drugs in the blood Example modeling representations Glycocalyx EC cell junctions Microvessel w/ outlined EC border Basement membrane (connective tissue) Interstitial Transport (Transport of the interstitial fluid) Lymph and interstitial fluid (ISF) • Lymph is formed when fluid that lies in the interstices of tissues (ISF) is collected and transported through lymph vessels. • Lymph vessels empty into the right or the left subclavian vein, where it mixes back with blood and is recirculated. • Composition of ISF continually changes as the blood and the surrounding cells exchange substances with the interstitial fluid. • ISF is essentially serum w/ WBCs Lymph emptied into tissue space collected by lymph vessels Fluid exits microvessels bc hydrostatic pressure of vessel exceeds osmotic pressure of tissue Starling Forces Drugs entering the ISF is a major step of circulating drugs reaching tissue Once in ISF drug must move around – Interstitial Transport Molecules move in tissue space by a combination of diffusion and convection • Diffusion is the net movement of a substance (e.g., an atom, ion or molecule) from a region of high concentration to a region of low concentration. • Convection is the concerted, collective movement of groups or aggregates of molecules within fluids Analogy of a sailing ship • In the absence of wind the ship drifts in the direction of the currents – Analogous to the motion of molecules from high to low concentration away from vessel • In the presence of wind the ship moves faster that the current and can even sail opposite to the current – Analogous to molecules moving (convecting) across vessel wall against the osmotic gradient L is the characteristic length n is the local flow velocity D is the diffusion coefficient Convection Lv Peclet Number = ~ Diffusion D Mol. MW D (cm2/s) tD(min) tC(min) Oxygen Glucose Fab’ Antibody DNA 32 180 50,000 150,000 4 ´106 2 ´10-5 2 ´10-6 3 ´10-7 1 ´10-8 1 ´10-9 0.1 0.8 5.6 166.7 1666.7 3.3 3.3 3.3 3.3 3.3 tD/tC= Pe 0.03 0.25 1.67 50 500 tDiffusion = L2/D, tConvection = L/v Assuming: v = 0.5 µm/sec, L = 100 mm Convection is important for macromolecular transport while diffusion is the major mechanism of the transport of small molecules. Interstitial fluid transport (Baxter, et al., Microvasc Res, 37: 77-104, 1989; Netti, et al., Cancer Res, 55: 5451-5458, 1995; Truskey et al., Transport Phenomena in Biological Systems, 2nd Ed., 2009) General approach: mass balance and momentum balance. Curl is a measure of field rotation using the right hand rule W rotation (curl>0) No rotation (curl=0) CW rotation (curl<0) Cyclone in Northern hemisphere Waterfall Cyclone in Southern hemisphere Divergence – 3D vector change in quantity wrt distance Source (viv>0) Sink (div<0) Steady state (div=0) Gradient – scalar change in quantity wrt distance Concentration Gradient Pressure Gradient Gradient of light on wall Rate of drug accumulation in ISF is equal to difference between the rate of drug that extravasates into tissue FV minus the rate of drug that is drained by the lymph FL u v (1 ) v L t where v: rate of fluid extravasation from blood vessels per unit volume, L: rate of lymphatic drainage per unit volume, : fractional volume of fluid in tissues, v : velocity of the interstitial fluid, u : solid tissue displacement. Transport across microvessels v J v LPv S v [ pv pi v ] V V J L LPL S L L [ pi pL L ] V V (blood vessel) (lymph vessel) Osmotic pressure difference terms v v ( v i ) L L ( i L ) Note: It may not be valid for continuous capillary at steady state but still be useful for transient delivery or for transport across leaky vessels (i.e., no osmotic pressure difference) The rate that ISF moves through tissue is a function of the tissue permeability (k), fluid viscosity (m), and the pressure gradient ( p) (Generalized Biot's law, 1856) u k v pi Kpi t m where: µ: viscosity of the fluid, k = K µ, specific permeability of porous medium, K: hydraulic conductivity of tissues, pi: gradient of IFP. ® ev =- k m Ñpi Darcy’s law Fluid transport in solid tumors at steady state (no sources or sinks) v v L v K p K p v L 2 (mass balance) (fluid momentum balance, Darcy’s law) (governing equation) K=hydraulic permeability of tissue, p is pressure, F rate of fluid extravisation and lymph drainage Simplified version of ISF pressure in 1D Ñ p = ¶ p / ¶x 2 2 2 (div squared in 1D) Governing Equation reduces to -Kd2p/dx2=FV-FL K=hydraulic permeability of tissue, d2p/dx2 is the second derivative ISF pressure p wrt x, FV-FL is the difference in the rate of fluid extravisation and lymph drainage Blood vessel FV ISF pressure x Lymph FL vessel Parameters That Govern Drug Transport In Tissues (P, LP, p, ) Drugs Cells Uptake (Nr, Vmax, Km) Microvessel Diffusion (c, D) Binding (kf, kr , Nr) Convection (p, K, ) Available volume fraction (KAV, ) Vessel wall (v, p, R) Consider example of bolus IV injection of drug Residence time of drug in ISF. How do these factors affect the shape of this curve? Tissue Concentration Residence Clearance Convection v. diffusion? Vessel permeability? Fluid viscosity? Hydraulic conductivity? Hydrostatic pressure gradient? Percent porosity of tissue? Osmotic pressure gradient? Filtration rate? Clearance rate (lymph uptake)? Molecular size? Molecular solubility in water? Cellular uptake? Accumulation Time